1. Field of the Invention
The present invention relates to an ink jet recording head and a method for manufacturing the same, and more particularly, relates to a structure of an electrical connecting portion for supplying electrical power and electrical signals to an ink jet recording head.
2. Description of the Related Art
A method in which electrodes on the surface of a semiconductor substrate and electrodes on the surface of a mounting board are connected with bumps is known and referred to as a “flip chip method”. Since high-density mounting is made possible by the flip chip method, this method is considered to be effective for electrical connection of semiconductor substrates, the number of input/output terminals of which has been increasing, and which have tended to be miniaturized in recent years.
A typical known process for forming a bump will be described below with reference to FIGS. 7A to 7H.
(1) An insulating film 203 is formed over a semiconductor substrate 201 on which an electrode pad 202 composed of aluminum is disposed such that a portion of the electrode pad 202 is exposed (FIG. 7A). The exposed portion of the electrode pad 202 corresponds to a bump-forming portion.
(2) A high-melting-point metal layer 204 is formed on the entire surface of the semiconductor substrate 201 so as to cover the exposed electrode 202 in order to improve the adhesion between the electrode 202 and a bump to be formed (FIG. 7B).
(3) A plating conductive layer 205 is formed thereon (FIG. 7C).
(4) A photosensitive resin layer 206 is formed further thereon (FIG. 7D).
(5) In order to form a bump 207, the photosensitive resin layer 206 is subjected to patterning to provide a hole in a portion of the photosensitive resin layer 206 where the bump 207 is to be formed (FIG. 7E).
(6) The bump 207 is formed by electrolytic plating in the hole defined in the photosensitive resin layer 206 (FIG. 7F).
(7) The unwanted photosensitive resin layer 206 is removed (FIG. 7G).
(8) The plating conductive layer 205 and the high-melting-point metal layer 204 remaining around the bump 207 are removed by dissolution with a solvent (FIG. 7H).
In a head substrate used for an ink jet recording head, a gold bump is used as the bump 207. The periphery of the gold bump is desirably covered with a protective film for the reasons described below. Firstly, the protective film is provided in order to prevent the high-melting-point metal layer 204 under the bump 207 from becoming brittle due to side etching which may occur in the step (8) in the bump formation process described above in which the high-melting-point metal layer 204 is removed with the solvent. Secondly, the protective film is provided in order to take measures to a possible problem in which ink reaches an electrode wiring layer located under the bump 207 to cause corrosion depending on an ink material which will be newly developed or the compositional ratio of the material.
In order to solve the problems described above, a bump formation process in which the periphery of the side face of a bump is covered with a photosensitive resin layer is known (refer to Japanese Patent Laid-Open No. 2004-296497). However, in the bump formation process described in the laid-open publication, the step (7) in the bump formation process described above must be changed to a step in which, while allowing a portion of the photosensitive resin layer 206 serving as a protective film in contact with the periphery of the side face of the bump 207 to remain, only the unwanted portion of the photosensitive resin layer 206 is removed. Specifically, an additional step is required in which a resist material is applied to mask the bump 207 and a portion of photosensitive resin layer 206 serving as a protective film, and the resist material is subjected to patterning, exposure, and development. As described above, when the existing bump protection technique is applied to the known method for manufacturing an ink jet recording head, the total number of manufacturing steps is increased, which is a problem.